1. Field of the Invention
The present invention relates to novel recombinant antibodies targeting the HER2 receptor and compositions comprising two or more of these antibodies for use in human cancer therapy.
2. Background of the Invention
The epidermal growth factor receptor (EGFR) family (also known as the ErbB family) is a subgroup of the receptor tyrosine kinases (RTKs) and consists of four members: EGFR/ErbB, HER2/ErbB2, HER3/ErbB3 and HER4/ErbB4. The members of the EGFR family are closely related single-chain modular glycoproteins with an extracellular ligand binding region, a single transmembrane domain and an intracellular tyrosine kinase (reviewed in Ferguson (2008) Annu Rev Biophys. 37: 353-373). In normal physiological settings the ErbB family regulates key events in coordination of cell growth, differentiation and migration (Citri et al. (2006) Nat Rev Mol Cell Biol. 7: 505-516). EGFR, HER2 and HER3 are believed to play crucial roles in the malignant transformation of normal cells and in the continued growth of cancer cells. EGFR and HER2 have been found to be overexpressed by many epithelial cancers (Slamon et al. (1987) Science, 235: 177-182; Arteaga (2002) Oncologist 7 Suppl 4: 31-39; Bodey et al. (1997) Anticancer Res. 17: 1319-1330; Rajkumar et al. (1996) J Pathol. 179: 381-385). Overexpression of EGFR and HER2 has furthermore been linked to disease progression, reduced survival, poor response and chemotherapy resistance in several human epithelial cancers (Slamon et al. (1987) supra; Baselga et al. (2002) Oncologist 7 Suppl 4: 2-8).
Human epidermal growth factor receptor 2 (HER2, also known as ErbB2 or Neu; UniProtKB/Swiss-Prot No. P04626) consists of 1233 amino acids and is structurally similar to EGFR with an extracellular domain consisting of four subdomains I-IV, a transmembrane domain, a juxtamembrane domain, an intracellular cytoplasmic tyrosine kinase and a regulatory C-terminal domain (Yamamoto et al. (1986) Nature 319: 230-234).
HER2 is the only member of the ErbB family that does not bind known ligands (Klapper et al. (1999) Proc Natl Acad Sci USA 96: 4995-5000). HER2 is instead activated via formation of heteromeric complexes with other ErbB family members and thereby indirectly regulated by EGFR and HER3 ligands (reviewed in Yarden et al. (2001) Nat Rev Mol Cell Biol. 2: 127-137). HER2 is the preferred heterodimerization partner of the three other ErbB receptors (Graus-Porta et al. (1997) EMBO J 16: 1647-1655; Tzahar et al. (1996) Mol Cell Biol. 16: 5276-5287), enhancing the affinity of the other ErbB receptors for their ligands by slowing down the rate of ligand-receptor complex dissociation, whereby HER2 enhances and prolongs signaling (Pedersen et al. (2009) Mol Cancer Res. 7: 275-284). Heterodimerization of HER2 and another ligand-bound receptor of the ErbB family induces cross-phosphorylation, leading to phosphorylation of the C-terminal amino acids. These in turns serve as scaffolds for signaling molecules (King et al. (1988) EMBO J 7:1647-1651). The most active HER2 heterodimer is the HER2-HER3 complex (Pinkas-Kramarski et al. (1996) EMBO J 15: 2452-2467), where HER2 complements the kinase-deficient HER3 by providing an active kinase (Guy et al. (1994) Proc Natl Acad Sci USA 91: 8132-8136.). In contrast to EGFR, HER2 is internalization resistant (Hommelgaard et al. (2004) Mol Biol Cell 15: 1557-1567), escaping lysosomal degradation and thereby remaining at the plasma membrane.
The primary role of HER2 in normal tissues appears to be modulation of signaling initiated through a ligand-bound ErbB receptor. Like EGFR, HER2 is primarily expressed by epithelial cells (reviewed in Freudenberg et al. (2009) Exp Mol. Pathol. 87: 1-11) and has been found to have a non-oncogenic role in regulating growth, differentiation, apoptosis and remodeling in normal mammary gland development (Troyer et al. (2001) J Mammary Gland Biol Neoplasia 6: 7-21). As it is the case for EGFR, an excess of HER2 on the cell surface causes transformation of epithelial cells from multiple tissues (Freudenberg et al. (2009) supra). HER2 amplification and overexpression have been reported in a range of human tumors, including 20-30% of invasive ductal carcinomas, and is a well recognized predictor of poor clinical outcome with reduced overall survival rates (Slamon et al. (1987) supra; Ravdin et al. (1995) Gene 159: 19-27). High levels of HER2 can be readily detected in human breast tissues that show early signs of transformation but have not yet fully transformed, indicating the important role of HER2 in the early malignant transformation (Freudenberg et al. (2009) supra). High levels of HER2 have also been implicated in other epithelial cancers such as colorectal, ovarian, pancreatic, lung, and urothelial cancers (Freudenberg et al. (2009) supra). HER2 activation induces uncontrolled proliferation, protects against apoptosis, and disrupts normal epithelial organization (Muthuswamy et al. (2001) Nat Cell Biol. 3: 785-792). Furthermore, HER2 is expressed by metastatic cells and may play a role in cancer cell motility (De Potter (1994) Hum Pathol. 25: 1264-1268).
EGFR and HER2 are validated cancer targets and both monoclonal antibodies and small molecule inhibitors targeting these receptors have been approved for the treatment of various cancers. However, patients who initially respond to these therapies often relapse due to evolvement of acquired resistance (Pao et al. (2005) PLoS Med 2: e73). The monoclonal antibody trastuzumab (marketed as Herceptin®) targets HER2 and is used for treatment of breast cancer in which the HER2 receptor is overexpressed. In January 2010 Herceptin was approved in the European Union in combination with chemotherapy for use in patients with HER2-positive metastatic stomach (gastric) cancer. Another monoclonal antibody directed in part against the HER2 receptor, pertuzumab, is currently in various clinical trials. In contrast to trastuzumab, which acts by binding to HER2 and thereby blocking its function, pertuzumab is a HER dimerization inhibitor which inhibits dimerization of HER2 to HER3 and the other EGFR receptors.
Since pertuzumab is still in clinical trials, the extent to which it may ultimately prove to be clinically beneficial is still unknown. For trastuzumab, while it has shown clinical benefits in terms of e.g. prolonged survival in connection with chemotherapy compared to chemotherapy alone, a majority of HER2 positive breast cancer patients were nevertheless found to be non-responders (45% overall response rate for Herceptin+chemotherapy vs. 29% for chemotherapy alone; Prescribing Information for Herceptin, Genentech, March 2009). Similar results are described by Slamon et al. in N Engl J Med (2001), 344(11):783-92, who also describe that the combination of Herceptin and chemotherapy resulted in a lower rate of death at 1 year compared to chemotherapy alone (22% vs. 33%, P=0.008) and a longer median survival (25.1 vs. 20.3 months, P=0.046). Thus, while monoclonal antibody therapy directed against HER2 has been shown to provide improved treatment in e.g. metastatic breast cancers that overexpress HER2, there is still considerable room for improvement.